It is known to produce compounds having the formula (R)X.sub.m-p A.sub.p (hereinafter Compound III) as defined below by the reaction sequence: ##STR1## wherein:
X is halide;
R contains from 1 to 8 carbon atoms, can be substituted or unsubstituted, and is straight or branched chain alkyl, cycloaliphatic, aralkyl, alkylene, alkenyl, alkenylene, alkynyl or alkynylene with the proviso that X is not attached to a carbon atom having a double bond;
A.sup.- is a monovalent anion soft base selected from the group consisting of halide other than X, 3CN.sup.-, SH.sup.-, SO.sub.2 H.sup.-, R.sub.2 PO.sub.4, R.sub.2 PO.sub.3.sup.-, PF.sub.6.sup.-, and [SP(Z)(OR.sup.1).sub.2 ].sup.- wherein R.sup.1 is lower alkyl and Z is sulfur or oxygen;
M is an alkali metal or NH.sub.4.sup.+ ;
m is an integer from 1 to 3 with the proviso that m is 1 or 2 when R has one carbon; and
p is an integer from 1 to m.
As used herein, a soft base means an anion of a relatively large size and having a diffused charge. See: (1) Pearson, R. G., Survey of Progress in Chemistry, 5 (1969, Academic Press); (2) Lowry, T. H., and Richardson, K. S., Mechanism and Theory in Organic Chemistry, Harper & Row, New York, NY (1976) pp. 165-168; 374-375. Soft bases having the formulas SCN.sup." and [SP(Z) (OR.sup.1).sub.2 ].sup.- are disclosed in U.S. Pat. Nos. 4,087,451, and 3,014,058, respectively. As used herein, lower alkyl means an alkyl having from 1 to 4 carbon atoms.
The R group may be substituted with halide, nitro, cyano, and other conventional substituents which do not interfere with the reaction.
Typical of such compounds is methylene bisthiocyanate which is well-known for use limiting the growth and reproduction of microorganisms. It is particularly of use in the paper industry to prevent the growth of fungi, bacteria, and other microorganisms or enzymes produced by the growth. (See, U.S. Pat. No. 3,306,810.)
Traditionally, this reaction has been carried out in aqueous solvent although other solvents, such as cyclic aromatics have been used. (See, U.S. Pat. 3,524,871 and British Published Patent Application 2,118,160a.)
A major problem with the prior art process is that the by-product metal halide MX, e.g., sodium bromide, is left in the mother liquor. This is a waste material since the compound (R)X.sub.m-p A.sub.p precipitates out and is formulated in a separate step from the synthesis. For example, when compound III is methylene bisthiocyanate prepared from CH.sub.2 Br.sub.2 or sodium or ammonium thiocyanate, the mother liquor, after separation of the (R)X.sub.m-p A.sub.p contains about 45% of the metal halide, about 3% of the reactant MA, and from 0.5-1% of the (R)X.sub.m-p A.sub.p. This is a hazardous waste material. The (R)X.sub.m-p A.sub.p which is precipitated is then treated in an aqueous dispersion or a nonaqueous solvent, such as, dimethyl formamide, alcohols, and the like. The aqueous dispersion is undesirable because of its great instability resulting from sudden changes in temperature. It is desirable that it be maintained as a homogeneous solution for use.